The report is prepared for the general information of shareholders.

It is authorized for distribution to prospective investors only when preceded or accompanied by a current prospectus.

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LETTER FROM THE EXECUTIVE CHAIR

Dear Shareholders:

During the first quarter of 2020, market volatility reached levels not seen since the global financial crisis. Optimism heading into the year — on receding trade and

geopolitical risk along with easier central bank policies — was overwhelmed in February as the health effects of a novel coronavirus, COVID-19, spread beyond China’s borders, impacting over 100 countries. The global pandemic prompted many governments to take drastic action to arrest the spread of the virus, such as quarantines, school and business closures and prohibitions on large public gatherings. While these are important steps to protect the public health, they come at a cost: rising market volatility and expectations of falling global economic growth.

The situation remains uncertain given that countries differ in terms of the way they are responding to the outbreak and the resources

they have at their disposal to fight it. From a market perspective, global central banks have taken aggressive, coordinated steps to cushion the economic impact of the fallout related to the virus, and governments are undertaking considerable fiscal stimulus. As uncertainty recedes, these measures can help create a supportive environment and encourage economic recovery. Occurrences such as the COVID-19 outbreak demonstrate the importance of having a deep understanding of company fundamentals, and our global research platform has been built to do just that.

Here at MFS®, we aim to help our clients navigate the growing complexity of the markets and world economies. Our long-term investment philosophy and commitment to the responsible allocation of capital allow us to tune out the noise and uncover what we believe are the best, most durable investment opportunities in the market. Through our powerful global investment platform, we combine collective expertise, thoughtful risk management, and long-term discipline to create sustainable value for investors.

Respectfully,

Robert J. Manning

Executive Chair

MFS Investment Management

March 18, 2020

The opinions expressed in this letter are subject to change and may not be relied upon for investment advice. No forecasts can be guaranteed.

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PORTFOLIO COMPOSITION

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Portfolio Composition – continued

Where the fund holds convertible bonds, they are treated as part of the equity portion of the portfolio.

The fund invests a portion of its assets in the MFS High Yield Pooled Portfolio. Percentages include the indirect exposure to the underlying holdings, including investments in money market funds and Other, of the MFS High Yield Pooled Portfolio and not the direct exposure from investing in the MFS High Yield Pooled Portfolio itself.

Cash & Cash Equivalents includes any direct exposure to cash, direct and indirect exposure to investments in money market funds, cash equivalents, short-term securities, and other assets less liabilities. Please see the Statement of Assets and Liabilities for additional information related to the fund’s direct cash position and other assets and liabilities.

Other includes the direct and indirect equivalent exposure from currency derivatives and/or any offsets to derivative positions.

Percentages are based on net assets as of January 31, 2020.

The portfolio is actively managed and current holdings may be different.

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MANAGEMENT REVIEW

Summary of Results

For the twelve months ended January 31, 2020, Class A shares of the MFS Global High Yield Fund (fund) provided a total return of 9.59%, at net asset value. This compares with a return of 10.55% for the fund’s benchmark, the ICE BofA Global High Yield – Constrained Index (USD Hedged) (formerly the BofA Global High Yield – Constrained Index (USD Hedged)).

In addition to investing directly in portfolio securities, the fund also invests indirectly in portfolio securities through investment in the MFS High Yield Pooled Portfolio, a mutual fund also advised by MFS. The discussion below reflects both the fund’s direct and indirect investments.

Market Environment

Fading fears of a near-term global recession, the announcement of a partial trade deal between the United States and China and the decline in uncertainty over Brexit helped bolster market sentiment late in the period, although an outbreak of coronavirus emanating from central China contributed to a bout of volatility at period’s end. Markets had anticipated that dissipating headwinds would lead to a rebound in global growth and trade in early 2020, but supply chain disruptions linked to the virus are now calling that assumption into question.

The headwinds from trade and geopolitical uncertainty, along with declining inflationary pressures, prompted the US Federal Reserve to adopt a more dovish posture beginning in early 2019, resulting in the first interest rate cut in over a decade at the end of July, followed by additional cuts in September and October. The Fed’s actions led to a sharp decline in long-term interest rates during the period’s second half, causing the inversion of portions of the US Treasury yield curve for a time. Amid an improvement in risk sentiment in the fourth quarter of 2019, and indications of a bottoming in growth and a potential upturn in activity, the Fed indicated in October that further rate cuts were unlikely unless the outlook for the economy materially worsened.

Globally, central banks have tilted more dovish as well, with the European Central Bank having unveiled a package of easing measures, which included putting overnight rates deeper into negative territory, restarting its bond-buying program and lengthening the term of cheap loans to banks to three years from two. The central banks of India and Australia were among those that cut interest rates several times in recent months, while China began to loosen policy late in the period.

The more dovish Fed in 2019 helped improve conditions in emerging markets. Notwithstanding the periodic headwinds on market sentiment from significant trade friction between the US and China over much of the year, emerging market hard currency debt and local rates benefited from relatively cheap valuations at the beginning of the period along with easier global monetary conditions. These factors, plus the fading of certain global risk factors mentioned above, hastened spread tightening in the latter part of the period. At the same time, idiosyncratic risks spiked in some countries (e.g., Argentina and Lebanon), which contributed to an increased dispersion in performance among sovereign fixed income assets.

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Management Review – continued

Detractors from Performance

Relative to the ICE BofA Global High Yield – Constrained Index (USD Hedged), the fund’s shorter relative duration ^(d) exposure detracted from performance as interest rates generally declined over the reporting period. Additionally, an out-of-benchmark exposure to the sovereign sector, and a greater exposure to the electric sector, held back relative returns. Bond selection within both the basic industry and communications sectors further weighed on the fund’s relative results.

Top individual detractors for the reporting period included the fund’s overweight exposures to Argentina (sovereign), investment services provider Northwest Acquisitions (basic industry), independent exploration and production company Alta Mesa Resources ^(h) (energy) and Stoneway Capital (electric).

Contributors to Performance

Security selection was an overall positive factor that benefited relative returns. From a quality perspective, bond selection within “BB” rated ^(r) issuers helped relative results. From a sector perspective, selection within the consumer non-cyclical, consumer cyclical and energy sectors supported relative performance.

The fund’s asset allocation decisions, overall, were another factor that positively impacted relative results. Notably, the fund’s lesser exposure to the energy sector and its greater exposure to the capital goods sector contributed to relative returns.

Top individual contributors for the reporting period included the fund’s overweight exposures to Ukraine (sovereign), Turkey (sovereign), instant lottery tickets producer Scientific Games International (consumer cyclicals) and new home construction and development services company Mattamy Group (consumer cyclicals).

Respectfully,

Portfolio Manager(s)

David Cole, Matt Ryan, and Michael Skatrud

The views expressed in this report are those of the portfolio manager(s) only through the end of the period of the report as stated on the cover and do not necessarily reflect the views of MFS or any other person in the MFS organization. These views are subject to change at any time based on market or other conditions, and MFS disclaims any responsibility to update such views. These views may not be relied upon as investment advice or an indication of trading intent on behalf of any MFS portfolio. References to specific securities are not recommendations of such securities, and may not be representative of any MFS portfolio’s current or future investments.

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PERFORMANCE SUMMARY THROUGH 1/31/20

The following chart illustrates a representative class of the fund’s historical performance in comparison to its benchmark(s). Performance results include the deduction of the maximum applicable sales charge and reflect the percentage change in net asset value, including reinvestment of dividends and capital gains distributions. The performance of other share classes will be greater than or less than that of the class depicted below. Benchmarks are unmanaged and may not be invested in directly. Benchmark returns do not reflect sales charges, commissions or expenses. (See Notes to Performance Summary.)

Performance data shown represents past performance and is no guarantee of future results. Investment return and principal value fluctuate so your shares, when sold, may be worth more or less than the original cost; current performance may be lower or higher than quoted. The performance shown does not reflect the deduction of taxes, if any, that a shareholder would pay on fund distributions or the redemption of fund shares.

Growth of a Hypothetical $10,000 Investment

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Performance Summary – continued

Total Returns through 1/31/20

Average annual without sales charge

Benchmark Definition(s)

ICE BofA Global High Yield – Constrained Index (USD Hedged) (formerly BofA Global High Yield – Constrained Index (USD Hedged)) – tracks the performance of below investment grade corporate debt of issuers domiciled in countries having an investment grade foreign currency long-term debt rating (based on an average of Moody’s and S&P). The Index is weighted by outstanding issuance, but constrained such that the percentage of any one issuer may not represent more than 2% of the Index. Source ICE Data Indices, LLC (“ICE Data”), is used with permission. ICE Data, its affiliates and their respective third party suppliers disclaim any and all warranties and representations, express and/or implied, including any warranties of merchantability or fitness for a particular purpose or use, including the indices, index data and any data included in, related to, or derived therefrom. Neither ICE Data, its affiliates nor their respective third party suppliers shall be subject to any damages or liability with respect the adequacy, accuracy, timeliness or completeness of the indices or the index data or any component thereof, and the indices and the index data and all components thereof are provided on

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Performance Summary – continued

an “as is” basis and your use is at your own risk. ICE Data, its affiliates and their respective third party suppliers do not sponsor, endorse or recommend MFS, or any of its products or services.

It is not possible to invest directly in an index.

Notes to Performance Summary

Average annual total return represents the average annual change in value for each share class for the periods presented.

Performance results reflect any applicable expense subsidies and waivers in effect during the periods shown. Without such subsidies and waivers the fund’s performance results would be less favorable. Please see the prospectus and financial statements for complete details.

Performance results do not include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles and may differ from amounts reported in the financial highlights.

From time to time the fund may receive proceeds from litigation settlements, without which performance would be lower.

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EXPENSE TABLE

Fund expenses borne by the shareholders during the period, August 1, 2019 through January 31, 2020

As a shareholder of the fund, you incur two types of costs: (1) transaction costs, including sales charges (loads) on certain purchase or redemption payments, and (2) ongoing costs, including management fees; distribution and service (12b-1) fees; and other fund expenses. This example is intended to help you understand your ongoing costs (in dollars) of investing in the fund and to compare these costs with the ongoing costs of investing in other mutual funds.

In addition to the fees and expenses which the fund bears directly, the fund indirectly bears a pro rata share of the fees and expenses of the MFS High Yield Pooled Portfolio, an underlying MFS Pooled Portfolio in which the fund invests. MFS Pooled Portfolios are mutual funds advised by MFS that do not pay management fees to MFS but do incur investment and operating costs. If these transactional and indirect costs were included, your costs would have been higher.

The example is based on an investment of $1,000 invested at the beginning of the period and held for the entire period August 1, 2019 through January 31, 2020.

Actual Expenses

The first line for each share class in the following table provides information about actual account values and actual expenses. You may use the information in this line, together with the amount you invested, to estimate the expenses that you paid over the period. Simply divide your account value by $1,000 (for example, an $8,600 account value divided by $1,000 = 8.6), then multiply the result by the number in the first line under the heading entitled “Expenses Paid During Period” to estimate the expenses you paid on your account during this period.

Hypothetical Example for Comparison Purposes

The second line for each share class in the following table provides information about hypothetical account values and hypothetical expenses based on the fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses, which is not the fund’s actual return. The hypothetical account values and expenses may not be used to estimate the actual ending account balance or expenses you paid for the period. You may use this information to compare the ongoing costs of investing in the fund and other funds. To do so, compare this 5% hypothetical example with the 5% hypothetical examples that appear in the shareholder reports of the other funds.

Please note that the expenses shown in the table are meant to highlight your ongoing costs only and do not reflect any transactional costs, such as sales charges (loads). Therefore, the second line for each share class in the table is useful in comparing ongoing costs only, and will not help you determine the relative total costs of owning different funds. In addition, if these transactional costs were included, your costs would have been higher.

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Expense Table – continued

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Portfolio of Investments – continued

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The following abbreviations are used in this report and are defined:

Abbreviations indicate amounts shown in currencies other than the U.S. dollar. All amounts are stated in U.S. dollars unless otherwise indicated. A list of abbreviations is shown below:

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Portfolio of Investments – continued

Forward Foreign Currency Exchange Contracts – continued